JP2006270128A - Method of detecting sample defect - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detection method, which after forming a plated layer on a sample, is capable of immediately detecting defects thereof. <P>SOLUTION: The detection method is a defect detection method for detecting defects of the sample, where a upper-plated layer (60) is formed on an SiO<SB>2</SB>layer (62) provided with trench portions. This method is such that an electron beam (63), emitted from an electron gun, is narrowed down to be made to pass through the SiO<SB>2</SB>layer of the sample, and the electron beam is made incident on the copper plated layer at the bottom of the trench portions in the SiO<SB>2</SB>layer to be scanned. Secondary electrons (64 and 68), emitted from the scanning points, are detected, and the defects of the sample are detected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron beam apparatus and a defect detection method using the electron beam apparatus, and more particularly to a method for detecting defects such as voids present in a film of a sample on which a film such as copper plating is formed.

For a sample (for example, a wafer) on which a film such as copper plating is formed, a defect such as a void may occur inside the copper plating layer. Conventionally, such defects inside the plated layer cannot be detected immediately after plating, and have been detected by performing potential contrast measurement after the wiring is completed. Moreover, the inspection of the sample surface after polishing with a CMP apparatus has been performed using an optical microscope.
On the other hand, when the electron gun is operating in the space charge limited region, it is known that the shot noise existing in the cathode current is multiplied by the shot noise reduction coefficient (Γ). Further, when the electron gun is an electron gun having a thermionic emission cathode, the brightness of the electron gun has a theoretical value called a Langmuir limit value, and it has been considered that this value cannot be greatly exceeded.

As described above, conventionally, defects inside the plating layer cannot be detected immediately after plating, but can only be detected after polishing by a CMP apparatus. Has been detected. Therefore, it was impossible to immediately investigate the cause and take prompt measures. Further, when the sample surface after being polished by the CMP apparatus is inspected by an optical microscope, it is difficult to find a defect having a size of 0.3 μm or less.
Furthermore, it is unclear whether the shot noise existing in the sample current can be reduced even if the shot noise existing in the cathode current is reduced by operating the electron gun in the space charge limited region. Further, when the electron gun is an electron gun having a thermionic emission cathode, there is a Langmuir limit value for the brightness of the electron gun. No one thought that high brightness could be achieved.
The present invention has been made in view of the conventional problems as described above, and one problem to be solved is to provide a method capable of detecting defects immediately after forming a plating layer on a sample. It is.
Another problem to be solved by the present invention is to provide a method for detecting defects in a sample at high speed.

The above problem is solved by the following means. That is, one of the inventions of the present application is a defect detection method for detecting defects in a sample in which a copper plating layer is formed on a SiO ₂ layer provided with a groove, and the electron beam emitted from an electron gun is narrowed down. The sample passes through the SiO ₂ layer of the sample, scans with the electron beam incident on the copper plating layer at the bottom of the groove of the SiO ₂ layer, detects secondary electrons emitted from the scanning point, and detects defects in the sample. I try to detect it.
In one embodiment of the present invention, the scanning is performed by deflecting the electron beam by a deflector.
In another embodiment of the present invention, the clock frequency of scanning by the deflector is 100 MHz or more.

An electron beam apparatus and a detection method capable of detecting defects immediately after forming a plating layer on a sample will be described with reference to the drawings.
In FIG. 1, an electron beam apparatus 1 is schematically shown. This electron beam apparatus 1 narrows down an electron beam emitted from an electron gun and irradiates the surface of a sample W (for example, a wafer on which a copper plating film is formed) W to be inspected with a finely focused electron beam. An optical system (hereinafter simply referred to as an optical system) 10, a detection system for detecting reflected electrons or secondary electrons emitted from the wafer W, and a sample stage 40 for holding the wafer W.
The optical system 10 includes an electron gun 11 that emits an electron beam under space charge limiting conditions, deflectors 12 and 13 that align the electron beam, a lens 14 that focuses the electron beam, an NA aperture 15, and a deflector 16. 1 and 17 and an objective lens 18, which are arranged in order along the optical axis A in the direction perpendicular to the surface of the wafer W with the electron gun 11 at the top, as shown in FIG. . The electron gun 11 has a thermionic emission type cathode (LaB ₆ cathode) 111, Wehnelt 112 and anode 113. The cathode 111 is formed in a conical shape whose tip is a part of a sphere having a curvature radius of 30 μm, and the cone angle of this conical shape is 90 degrees. The electron gun 11 is operated under a space charge limited condition, and the shot noise of the current emitted from the cathode is reduced by Γ (where Γ <1) times. Therefore, even when only an electron beam current of about 1/100 to 1/10000 of the cathode current can be obtained, the shot noise can be reduced by a factor of Γ. Further, the thermionic emission electron gun (LaB ₆ electron gun) can have the same luminance as a field emission (FE) electron gun, a thermal field emission (TFE) electron gun, or a Schottky electron gun, and has a cathode current of 980 μA. A luminance of 7.5 × 10 ⁸ A / cm ² sr is obtained at 20 kv.
The detection system includes a reflected electron detector 31 that detects reflected electrons emitted from the sample W, and a secondary electron detector 32 that detects secondary electrons emitted from the sample W.
The sample stage 40 has an electrostatic chuck 41 for fixing a wafer. The electrostatic chuck 41 is provided with electrodes divided into two portions, a central portion and a peripheral portion, on which a wafer W is mounted. Is fixed flat. Even a wafer that is warped upward can be chucked flat. The electrostatic chuck is fixed to an XY stage. The XY stage includes a magnescale 42 and a sensor 43 that measure a position in the X direction, and a sensor 44 that measures a position in the Y direction. The XY stage further moves the sample continuously in one axial direction and steps in the other axial direction.

In the electron beam apparatus 1 configured as described above, the electron beam emitted from the electron gun 11 creates an imaginary crossover behind the cathode 11. In this case, by setting the crossover to an imaginary crossover, it is possible to achieve ultra-high luminance far exceeding the limit value of Langmuir in a relatively wide range. A voltage to be applied to the Wehnelt 112 is determined so that an electron gun current capable of obtaining ultra-high brightness flows. The crossover passes through the deflectors 12 and 13 for axial alignment and the NA aperture 15, is focused by the lens 14 and the objective lens 18, is narrowed into a beam shape, is converged on the wafer W, and is reduced on the sample. Form an image. The wafer W can be scanned by deflecting the electron beam by the deflectors 16 and 17. In this case, the scanning clock frequency can be 100 MHz or more.
The secondary electrons emitted from the wafer W are separated from the optical axis A by the electric field of the detector 32 provided under the objective lens, and enter the secondary electron detector 32 through the trajectory indicated by B. Is detected.

FIG. 2 shows the secondary electron signal waveform of the wafer as a sample obtained by the electron beam apparatus, FIG. 2 (a) shows a part of the cross section of the wafer, and FIG. 2 (b) shows the cross section. The secondary electron signal waveform corresponding to the position of is shown. In FIG. 2A, reference numeral 60 is a copper plating layer, 61 is a defect such as a void formed in the copper plating layer, and 62 is a SiO ₂ layer. At the position where there is no defect with respect to the incidence of the electron beam 63, the signal waveform of the reflected electrons 64 is large as indicated by reference numerals 65 and 67 (FIG. 2B), while at the position where the defect exists, The signal waveform of the reflected electrons 64 is small as indicated by reference numeral 66 (FIG. 2B). In order for the reflected electrons 64 to emerge from the surface, it is necessary that the energy of the incident electron beam 63 enters a place where there is a defect, where it is backscattered and the electrons exit to the surface. Accordingly, the range (range) of the electron beam needs to be twice the thickness of the copper plating layer or film, and may be 2.5 times the range in consideration of some margin. On the other hand, secondary electrons 68 that are created immediately before the reflected electrons are emitted to the surface are detected by being emitted to the surface. In the present embodiment, since the thickness of the copper plating layer is 1 μm, the energy of the electron beam is 30 kev.
FIG. 3 shows an embodiment which is particularly effective when detecting voids existing in the deep part of the groove of the copper plating layer. 3A shows a part of the cross section of the wafer, and FIG. 3B shows a secondary electron signal waveform corresponding to the position of the cross section. In this embodiment, the electron beam 63 is incident from an angled direction rather than perpendicular to the surface of the wafer and passes through the SiO ₂ layer 62, thereby reducing the energy loss and allowing the electron beam to be plated with copper. Try to reach the bottom of the layer. In the case of this embodiment, at the position where the void 61 is present, the signal waveform of the reflected electrons 64 is indicated by reference numeral 66 (FIG. 3B), and the signal waveforms 65 and 67 at the position where there is no void, It is greatly distorted.

ここで、Ｉo：カソード電流、ｅ：電荷、Γ：空間電荷制限条件によるショット雑音低減係数、Δｆ：増幅器の帯域幅、をそれぞれ意味する。
試料に流れるビーム電流をＩ_Ｐとすると、Ｉ_Ｐはカソード電流Ｉoより十分小さいので、分配雑音が加わる。即ち、試料でのショット雑音は、

従って、試料電流に流れるショット雑音もΓ倍（Γ＜１）に低減されることが明らかとなった。 Next, an electron beam apparatus for inspecting defects on the surface of a sample such as a wafer polished by a CMP apparatus will be described with reference to FIG.
First, it will be examined how the shot noise of the electron beam emitted from the cathode becomes distribution noise when the beam current flowing through the sample is very small. The cathode shall operate under space charge limited conditions.
Shot noise in the electron beam emitted from the cathode is

Here, Io: cathode current, e: charge, Γ: shot noise reduction coefficient due to space charge limiting conditions, and Δf: amplifier bandwidth, respectively.
When the beam current flowing through the sample and I _P, since I _P is sufficiently smaller than the cathode current Io, partition noise is added. That is, shot noise at the sample is

Therefore, it has been clarified that the shot noise flowing in the sample current is also reduced by Γ times (Γ <1).

FIG. 4 schematically shows an electron beam apparatus 1 ′ for inspecting defects on the surface of a sample such as a wafer polished by a CMP apparatus. This electron beam apparatus 1 'narrows down the electron beam emitted from the electron gun, and on the surface of a sample W to be inspected (for example, a sample such as a wafer polished by a CMP apparatus) W. An irradiating optical system (hereinafter simply referred to as an optical system) 10 ′, a detection system 30 ′ for detecting secondary electrons emitted from the wafer W, and a sample stage 40 ′ for holding the wafer W are provided.
The optical system 10 ′ includes an electron gun 11 similar to the embodiment of FIG. 1 that emits an electron beam under space charge limiting conditions, deflectors 12 ′ and 13 ′ that align the electron beam, and a lens that focuses the electron beam. 14 ′, NA aperture 15 ′, deflectors 16 ′ and 17 ′, electromagnetic deflector 17 ″, and objective lens 18 ′, which are formed on the surface of wafer W as shown in FIG. They are arranged in order along the optical axis A ′ in the vertical direction with the electron gun 11 at the top. The electron gun 11 has a thermionic emission type cathode 111, a Wehnelt 112, and an anode 113 as in the embodiment of FIG. By increasing the bias of the Wehnelt 112 of the electron gun 11 to some extent, the electron gun 11 can operate under a space charge limited condition, and the current emitted from the cathode is shot noise is Γ (where Γ <1) times. Has been reduced. Further, a luminance of 7 × 10 ⁶ A / cm ² sr is obtained at 4.5 kv, and a luminance two or more orders of magnitude greater than the Langmuir limit value of 4.2 × 10 ⁵ A / cm ² sr is obtained. The NA aperture 15 'is provided on the sample side of the lens 14' so as to reduce the amount of backscattered electrons returning from here to the virtual cathode near the cathode.
The detection system includes a secondary electron detector 31 ′ that detects secondary electrons emitted from the sample W, and the secondary electron detector 31 ′ is disposed closer to the electron gun than the deflector 16 ′. .

  The sample stage 40 ′ has an electrostatic chuck 41 ′ for fixing the wafer W flat. The electrostatic chuck 41 ′ has a plurality of (three in this embodiment) holes 45 (one of them). Only one is shown). Push rods 46 are inserted into these holes. When unloading the wafer W from the electrostatic chuck 41 ′, the wafer is lifted by the three push rods 46, the unload arm 47 is placed under the wafer, and the electrostatic provided on the upper surface of the unload arm 47 This is performed by fixing with the chuck 48. A small electrostatic chuck 50 is attached to the push rod 46 via a weak coil spring 49, so that the wafer W can be safely loaded and unloaded. A spare chamber 53 is connected to the load / unload chamber 51 via a gate valve 52. The actuator 54 drives the unload arm 47. The unload arm 47, the electrostatic chuck 48, and the actuator 54 constitute a transfer device. The electrostatic chuck 41 ′ is fixed to an XY stage, and the XY stage includes a laser scale 55 and a sensor 56 for measuring the stage position in the X direction, and a laser scale 57 for measuring the stage position in the Y direction. Yes. The XY stage further moves the sample continuously in one axial direction and steps in the other axial direction.

In the electron beam apparatus 1 ′ having the above configuration, the electron gun 11 is adjusted so as to operate in the space charge limited region. Therefore, the shot noise generated by the electron beam can be greatly reduced. The electron beam emitted from the electron gun 11 is adjusted so as to optimally pass through the lens 14 ′ and the NA aperture 15 ′ by the deflectors 12 ′ and 13 ′ for axial alignment. The electron beam is further focused by the lens 14 ′ and the objective lens 18, narrowed into a point shape, and focused on the wafer W. The wafer W is scanned by deflecting the electron beam by the deflectors 16 ′ and 17 ′. In this case, as described above, a high luminance of 7 × 10 ⁶ A / cm ² sr or more is obtained, which is 10 times or more larger than the Langmuir limit value of 4.2 × 10 ⁵ A / cm ² sr. A beam current of 100 nA or more can be obtained with a beam diameter. Therefore, an S / N ratio of 20 is obtained even when scanning is performed at 100 MHz, and a resolution that can detect defects such as scratches on a polished surface of 0.1 μm or more is obtained.
The secondary electrons emitted from the wafer W are separated from the optical axis A by the electromagnetic deflector 17 ″, pass through the trajectory indicated by the symbol B ′, and enter the secondary electron detector 31 ′ to be detected. .

Next, a method for manufacturing a semiconductor device using the electron beam apparatus will be described with reference to FIGS.
FIG. 5 is a flowchart showing an embodiment of a semiconductor device manufacturing method. The process of this embodiment includes the following main processes.
(1) Wafer manufacturing process for manufacturing a wafer (or wafer preparation process for preparing a wafer)
(2) Mask manufacturing process for manufacturing a mask for manufacturing a mask used for exposure (or mask preparation process for preparing a mask)
(3) Wafer processing step for performing necessary processing on the wafer (4) Chip assembly step for cutting out the chips formed on the wafer one by one and making them operable (5) Chip inspection step for inspecting the completed chips Each of the above main processes is further composed of several sub-processes.

Among these main processes, the wafer processing process (3) has a decisive influence on the performance of the semiconductor device. In this process, designed circuit patterns are sequentially stacked on a wafer to form a large number of chips that operate as memories and MPUs. This wafer processing step includes the following steps.
(1) A thin film forming process for forming a dielectric thin film to be an insulating layer, a wiring part, or a metal thin film for forming an electrode part (using CVD, sputtering, etc.)
(2) Oxidation step for oxidizing the thin film layer and wafer substrate (3) Lithography step for forming a resist pattern using a mask (reticle) to selectively process the thin film layer and wafer substrate (4) According to the resist pattern Etching process for processing thin film layers and substrates (for example, using dry etching technology)
(5) Ion / impurity implantation / diffusion process (6) Resist stripping process (7) Process for inspecting the processed wafer The wafer processing process is repeated for the required number of layers to manufacture a semiconductor device that operates as designed.

FIG. 6 is a flowchart showing a lithography process which is the core of the wafer processing process of FIG. The lithography process includes the following processes.
(1) Resist coating step for coating a resist on the wafer on which the circuit pattern is formed in the previous step (2) Step for exposing the resist (3) Development step for developing the exposed resist to obtain a resist pattern ( 4) Annealing process for stabilizing the developed resist pattern The semiconductor device manufacturing process, wafer processing process, and lithography process are well known and will not require further explanation.
When the defect inspection method and the defect inspection apparatus according to the present invention are used in the inspection process of (7) above, even a semiconductor device having a fine pattern can be inspected with high throughput, so that 100% inspection can be performed and the yield of products can be improved. It is possible to prevent shipment of defective products.
〔The invention's effect〕

According to the electron beam apparatus and the detection method, the following effects can be obtained.
(1) An electron gun having a LaB ₆ cathode can obtain a high luminance of 7 × 10 ⁶ A / cm ² sr or more, and is 10 times or more larger than the Langmuir limit value 4.2 × 10 ⁵ A / cm ² sr. Therefore, a beam current of 100 nA or more can be obtained with an electron beam diameter of 100 nm. Therefore, an S / N ratio of 20 was obtained even when scanning at 100 MHz, and defects such as scratches on the polished surface of 0.1 μm or more could be detected.
(2) Since a thermionic emission electron gun is used under space charge limiting conditions and a shot noise reduction coefficient Γ of about 0.2 is obtained, signal contrast that detects defects such as voids existing in the copper plating layer A sufficient S / N ratio can be obtained even when the frequency is small or when scanning is performed at a high frequency such as 100 MHz.
(3) Since the electron beam is incident at an angle with respect to the sample surface, the distance through the copper layer is small, and the energy loss is reduced by reaching the deep part of the copper plating through the SiO ₂ layer. Since the beam reaches the bottom of the copper plating layer, it becomes easy to detect the void at the bottom.

It is a figure which shows typically the electron beam apparatus which can detect the defect immediately after forming a plating layer in a sample. It is a figure which shows a part of cross section of a wafer. It is a figure which shows the secondary electron signal waveform corresponding to the position of the cross section of a wafer. FIG. 3 is a view showing a part of a cross section of a wafer, showing an embodiment in which an electron beam is incident on the wafer surface at an angle. FIG. 6 is a diagram showing an embodiment in which an electron beam is incident on the wafer surface at an angle, and is a diagram showing a secondary electron signal waveform corresponding to the position of a cross section of the wafer. It is a figure which shows typically the electron beam apparatus which test | inspects the defect of sample surfaces, such as a wafer ground with the CMP apparatus. It is a flowchart which shows a device manufacturing process. It is a flowchart which shows a lithography process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 ': Electron beam apparatus 10, 10': Optical system 11: Electron gun 12, 12 ': Deflector 13, 13': Deflector 14, 14 ': Lens 16, 16': Deflector 17, 17 ' : Deflector 18, 18 ': Objective lens 31, 31': Detector 40, 40 ': Sample stage 41, 41': Electrostatic chuck 42: Magnescale 46: Push rod 51: Load / unload chamber 54: Actuator 55, 57: Laser scale

Claims (3)

A defect detection method for detecting defects in a sample in which a copper plating layer is formed on a SiO ₂ layer provided with a groove,
The electron beam emitted from the electron gun is narrowed down,
Pass through the SiO ₂ layer of the sample, scan by making an electron beam incident on the copper plating layer at the bottom of the groove of the SiO ₂ layer,
A defect detection method comprising: detecting a secondary electron emitted from the scanning point to detect a defect of a sample. The defect detection method according to claim 1, wherein the scanning is performed by deflecting the electron beam by a deflector. The defect detection method according to claim 2, wherein a scanning clock frequency by the deflector is 100 MHz or more.

Images